题目：

题解：

class Solution {
public:string multiply(string num1, string num2) {if (num1 == "0" || num2 == "0") {return "0";}int m = num1.size(), n = num2.size();auto ansArr = vector<int>(m + n);for (int i = m - 1; i >= 0; i--) {int x = num1.at(i) - '0';for (int j = n - 1; j >= 0; j--) {int y = num2.at(j) - '0';ansArr[i + j + 1] += x * y;}}for (int i = m + n - 1; i > 0; i--) {ansArr[i - 1] += ansArr[i] / 10;ansArr[i] %= 10;}int index = ansArr[0] == 0 ? 1 : 0;string ans;while (index < m + n) {ans.push_back(ansArr[index]);index++;}for (auto &c: ans) {c += '0';}return ans;}
};